Apply Hellion theme plugin-wide with multi-accent palette

Move from a local color stack inside Hellion-only surfaces to a
single push wrapping Plugin.Draw, so chat log, settings,
viewers, the file dialog and the wizard all render under the same
palette. The local Push() helper stays for explicit use, but the
two existing call sites (Privacy tab, FirstRunWizard) now drop
their local pushes — the global stack already covers them and
double-pushing would shift colors on every frame.

Palette grew from a single cyan accent into a three-tone HUD set:

  Primary cyan-teal (#00B8D4)  → buttons, checkboxes, slider grabs,
                                 separator hover/active.
  Secondary industrial amber   → scrollbar grab and resize-grip
  (#FFB300)                      hover/active highlights.
  Tertiary slate violet         → active title bars and active tabs
  (#7B61FF)                      so identity beats out the cyan
                                 accent without competing with it on
                                 action controls.

Surfaces are deep slate (#0E1A20 windows, #102027 children, #162831
frames) with steel borders (#37474F). Style variables flatten the
default Dalamud rounding into something more geometric: 4 px window
rounding, 2 px frame/grab/tab/scrollbar, 1 px borders.

A new Configuration.HellionThemeEnabled (default true) and a
matching Appearance section at the top of the Privacy tab let users
turn the whole thing off and fall back to the Dalamud default look.
The flag is checked once per frame in Plugin.Draw — `using
IDisposable? _ = ... ? PushGlobal() : null` — so disabling has zero
overhead beyond a bool check.

ChatTwo/Configuration.cs

@@ -66,6 +66,11 @@ public class Configuration : IPluginConfiguration
     // ChatTwo users skip it because the v6→v7 migration sets the flag.
     public bool FirstRunCompleted;
 
+    // Hellion Chat global ImGui theme — applied to every plugin window in
+    // Plugin.Draw. Default ON; users who prefer the upstream Dalamud look
+    // can flip this off in the Privacy tab.
+    public bool HellionThemeEnabled = true;
+
     public int GetRetentionDays(ChatType type)
     {
         if (RetentionPerChannelDays.TryGetValue(type, out var userOverride))
@@ -244,6 +249,7 @@ public class Configuration : IPluginConfiguration
         RetentionLastRunAt = other.RetentionLastRunAt;
 
         FirstRunCompleted = other.FirstRunCompleted;
+        HellionThemeEnabled = other.HellionThemeEnabled;
     }
 }